CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net Income	$ 382.4	$ 312.0	$ 1,068.0	$ 1,066.7
Foreign Currency Adjustments:
Foreign currency translation adjustments - Pre Tax	(193.6)	(52.4)	(178.7)	(203.2)
Foreign currency translation adjustment - Tax	0.0	0.0	0.0	0.0
Foreign currency translation adjustments - Net of Tax	(193.6)	(52.4)	(178.7)	(203.2)
Net gains on net investment hedges - Pre Tax	136.7	5.9	130.1	28.0
Net gains on net investment hedges, Tax	(34.0)	(1.8)	(33.1)	(7.4)
Net gains on net investment hedges, Net of Tax	102.7	4.1	97.0	20.6
Net investment hedges - reclassification of gains included in net income - Pre Tax	(1.0)	0.0	(1.0)	0.0
Net investment hedges - reclassification of gains included in net income - Tax	0.2	0.0	0.2	0.0
Net investment hedges - reclassification of gains included in net income - Net of Tax	(0.8)	0.0	(0.8)	0.0
Cash Flow Hedges:
Net realized and unrealized gain (loss) on cash flow hedges - Pre Tax			0.0	1.9
Net realized and unrealized gain (loss) on cash flow hedges - Tax			0.0	(0.4)
Net realized and unrealized gain (loss) on cash flow hedges - Net of Tax			0.0	1.5
Reclassification of (losses) gains included in net income - Pre Tax	0.1	(0.1)	0.2	(0.3)
Reclassification of (losses) gains included in net income - Tax	0.1	0.0	0.1	0.0
Reclassification of (losses) gains included in net income - Net of Tax	0.0	(0.1)	0.1	(0.3)
Pension and Other Retirement Benefits:
Amortization of actuarial losses and prior service costs included in net income - Pre Tax	0.8	1.1	2.4	3.5
Amortization of actuarial losses and prior service costs included in net income - Tax	(0.2)	(0.3)	(0.6)	(1.0)
Amortization of actuarial losses and prior service costs included in net income - Net of Tax	0.6	0.8	1.8	2.5
Net actuarial (losses) gains and prior service costs - Pre Tax			(1.7)	1.6
Net actuarial (losses) gains and prior service costs - Tax			0.4	(0.4)
Net actuarial (losses) gains and prior service costs - Net of Tax			(1.3)	1.2
Total other comprehensive (loss) income - Pre Tax	(57.0)	(45.5)	(48.7)	(168.5)
Total other comprehensive (loss)income - Tax	34.1	2.1	33.2	9.2
Other comprehensive income/(loss)	(91.1)	(47.6)	(81.9)	(177.7)
Comprehensive income	291.3	264.4	986.1	889.0
Less: comprehensive income (loss) attributable to noncontrolling interests	3.1	(8.4)	14.7	(2.7)
Comprehensive Income Attributable to Moody's	$ 288.2	$ 272.8	$ 971.4	$ 891.7